Past Events

Abstract

Quasi-particles and collective modes are two fundamental aspects that characterize a quantum mater in additional to its ground state features. For example, the low energy physics for Fermi liquid phase in He-III was featured not only by Fermionic quasi-particles near the chemical potential, but also by fruitful collective modes in the long wave length limit, including several different sound waves that can propagate through it under different circumstances. On the other hand, it is very difficult for sound waves to be carried by the electron liquid in the ordinary metals, due to the fact that long range Coulomb interaction among electrons will generate plasmon gap for ordinary electron density waves and thus prohibits the propagation of sound waves through the electron liquid. In the present paper, we propose an unique type of acoustic collective modes formed by Weyl fermions under the magnetic field, which is called chiral zero sound (CZS). The CZS only exists and propagates along an external magnetic field for Weyl semi-metal systems containing multiple-pairs of Weyl points. The sound velocity of CZS is proportional to the field strength in the weak field limit, whereas oscillates dramatically in the strong field limit generating completely new mechanism for quantum oscillations through the dynamics of neutral Bosonic excitation, which may manifests itself in the thermal conductivity measurements under magnetic field.

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